1. Field of the Invention
This invention relates to twisting tumbler locks and particularly to twisting tumbler locks as manufactured by Medeco Security Locks, Inc. of Salem, Virginia. Most particularly this invention relates to twisting tumbler cylinder locks manufactured by Medeco Security Locks, Inc. and designated as a "cam or switch lock".
2. Description of the Prior Art
Locks of the twisting-tumbler type are typified by the lock described and claimed in U.S. Pat. No. 3,499,302 granted to R. C. Spain et al. on Mar. 10, 1970, for cylinder lock, which patent is hereby incorporated by reference in its entirety. Such patent describes a cylinder lock having a cylinder shell and a key plug rotatably mounted therein. Slidably mounted in the key plug are a plurality of transversely extending tumblers each of which has a chiseled shaped bottom and a vertically extending groove. Above the tumblers are drivers. A key is inserted in the keyway of such lock, which key is bitted so as to cause the upper ends of the tumblers to all rest in the shear plane of the lock. However, the vertical positioning of the tumblers as above described does not necessarily unlock the lock described in the aforementioned Spain et al. patent. In addition to the vertical positioning, the Spain et al. patent requires that each of the tumblers be rotatably positioned to a particular angular position whereby to permit the movement into said vertically extending grooves of protrusions on a transversely movable side bar which side bar, in its extended position, extends across the shear plane of the lock to prevent rotation of the key plug relative to the cylinder shell. However, when all of the tumbler grooves are in alignment with their associated side bar protrusions, the side bar is free to move out of the shear plane of the Spain et al. lock whereby to unlock the lock, assuming the appropriate vertical positioning of the tumblers.
A lock of the type described by Spain et al. in the said aforementioned patent is commercially available under the trademark MEDECO as a mortise or rim cylinder lock and such a lock, somewhat modified from that structure described in the aforementioned patent, is described in a patent application of even date filed by the inventor hereof and George V. Iaccino, which application bears the same title as the title of the present application and is hereby incorporated by reference in its entirety.
As is true in both the Spain et al. patent previously mentioned and in the commercially available mortise and rim cylinder locks manufactured by Medeco Security Locks, Inc., the key plug is locked separately by two separate mechanisms, one being the bridging of the shear plane by the drivers and the other being the bridging of the shear plane by the side bar. Medeco Security Locks, Inc. manufactures a second form of lock commonly referred to as a cam or switch lock. This lock, which also operates on the twisting tumbler principle of the cylinder lock described in said Spain et al. patent, differs from the locks described in said patent and from the Medeco mortise and rim cylinder locks commercially available in that the vertical position of the tumblers does not directly provide a lock to prevent rotation between the key plug and the cylinder. The only lock in the cam or switch lock manufactured by Medeco Security Locks, Inc. is due to a bridging of the shear plane by the side bar. However, the vertical positioning of the tumblers is still critical to the unlocking of the lock, as is ture in the more common mortise and rim cylinder locks of Medeco, by virtue of the replacement of the tumbler grooves in the mortise and rim cylinder locks by a small radially extending holes in each tumbler in the cam or switch lock. The holes must receive the associated protuberance of the side bar in order to permit the side bar to move inwardly out of bridging relation with the shear plane and thus unlock the key plug from the lock cylinder shell. Since a small aperture is employed in the cam or switch lock, it will be obvious to those skilled in the art that the aperture must be vertically registered with its associated side bar protuberance as well as angularly registered therewith, whereby to cause the lock to require a key having bits with both the proper angulation and depth of bit cut as is true in the locks of the Spain et al. patent.
In the aforementioned application of even date, filed by the inventor hereof and his co-inventor George V. Iaccino, methods and apparatus for decoding Medeco locks sold as mortise and rim cylinder locks which locks are quite similar to the locks described and claimed in said aforementioned Spain et al. patent have been described and claimed. However, the methods and apparatus described therein are dependent in part at least on the presence of the longitudinally or vertically extending grooves in each of the tumblers, which grooves provide a hooking abutment for the angulation decoding method and apparatus described in said application of even date. Since such groove is not present in the cam or switch lock of the twisting tumbler type manufactured by Medeco Security Locks, Inc., the methods and apparatus of said co-pending application of Iaccino and Idoni will not operate on the Medeco cam and switch locks.
The present invention is directed to a separate method and apparatus for decoding such cam or switch locks manufactured by Medeco. The present invention is also directed to a modified form of cam or switch lock which will defeat the method and apparatus for decoding the standard Medeco cam and switch lock.